Screening cage

ABSTRACT

Electric screening cage comprising multifilarly helically wound wires connected to earth so that the earth-connected ends of each pair of adjacent wires are located at opposite ends of the cage.

United States Patent 1191 Holman I 1 July 16, 1974 SCREENING CAGE 2,754,415 7/1956 s611m1d1, Jr 336/170 x [76] Inventor: Benedict, Timotheus Johannes 3,158,774 11/1964 Flemmg et al. 335/210 x Holman, Emmasingel, Eindhoven, Netherlands FOREIGN PATENTS OR APPLICATIONS [22] May 1972 1,095,313 6/1961 Germany 335/210 [21] Appl. N0.: 252,938

Related US. Application Data [63] Continuation of Ser, No. 110,457, Jan. 28, 1971,

abandoned.

[30] Foreign Application Priority Data Feb. 18, 1970 Netherlands films [52] US. Cl. 335/213, 335/214 51 I111. (31. 11 011-5/00 [58] Field of Search 335/210, 213, 301, 214 v [56] References Cited 5 UNITED STATES PATENTS 10/1940 Hepp 335/214 Primary Examiner-George Harris 411mm Agent, or FirmFmnk R, Tritnri; Henry I Steckler [57] ABSTRACT Electric screening cage comprising multifilarly helically wound wires connected to earth so that the earth-connected ends of each pair of adjacent wires are located at opposite ends of the cage.

4 Claims, 3 Drawing Figures PATENTEDJUUBEIN 3.824.515

MEN 0F 2 I N VENTOR BENED ICTUS T. J. HOLMAN FIG.3

1 SCREENING CAGE This is a continuation of application Ser. No. 1 10,457 filed Jan. 28, 1971, now abandoned. I

This invention relates t'o'a device for electric screening, which does not disturb magnetic fields and which comprises a cylindrical cage composed mainly of electrically conductive material.

This kind of screening may be used in the deflection units of camera tubes between the line deflection coil and other parts such as the frame deflection coil and the target plate. It is important in this case that the electric screening should be effective at frequencies up to a few M Hz without disturbing the magnetic field of the line deflection coil. It is known to use for this purpose a thin metal screen within the deflection coil, for example, copper foil. In order to avoid eddy currents voids have to be provided therein. This is harmful to the screening effect and the manufacture is expensive. It is, moreover, difficult to secure connecting wires in a reliable manner to this thin metal foil for the requiredground-connection of the screen. A screening device comprising a helically wound wire connected to ground only at one end for avoiding magnetic short-circuit does not exhibit the said disadvantage, but this solution is only appropriate for low frequencies, for example, for screened supply transformers. For frequencies up to a few MHz a screening cage of this kind is only effective near the ground-connected end because, due to the inductance of the turns, the other end is not grounded for high frequencies. A reduction of the inductance by spacing the turns further apart has the disadvantage that the openings between the turns become larger,

which is detrimental to the screening effect.

An object of the invention is to provide a structure which is free of the aforesaid disadvantages.

According to the invention this is achieved by forming the cage from at least two multifilarly, helically wound wires, one end of each wire being connected to ground and the grounded ends of each pair of adjacent wires being located at opposite ends of the cylinder. This structure has an appearance similar to the bifilar coil shown in US. Pat. No. 2,026,308, FIG. 2, which coil serves, however, as a primary winding of a highfrequency transformer so that the resemblance only lies in the form and is not related to the function.

The invention will be described with reference to the accompanying FIGS. 1 and 2 in which two embodiments are shown in axial sectional views; and

FIG. 3 shows a screening coil in accordance with the invention disposed between deflection coils and about a camera tube.

The screening cage of FIG. 1 comprises two insulated wires 3 and 5, bifilarly wound to form a closed cylindrical sheath. The wire 5 is indicated in the Figure by a marking line for the sake of clarity.

In the wire 3 the end 7 is free and the end 9 may be directly connected to ground. In a similar manner the end 13 of the wire 5 is free and the end 15' is directly connected to ground, which is represented by the symbol. 17. For structural reasons it may be desirable to extend the'end 9 of wire 3 by means of a lead 19 and to connect it to ground together with the end 15 of wire 5 at a single point 17. The screening effect is not adversely affected as a result of this construction.

The advantages over a foil as a screening means are that no eddy currents can pass through the closed cylindrical wall, the structure is automatically provided with connecting wires for ground connection, and it is cheap. The advantages over a single, helically wound wire are that theturns of the wires 3 and 5, considered separately, are not in contact with each other so that the inductance is lower, while the openings in one helix are filled in by the turns of the other helix.

Moreover, the free end of each wire is grounded via the capacitance relative to the grounded end of the other wire for high frequencies so that the influence of the inductance is further reduced.

FIG. 2 shows one embodiment of a cage 21 formed by four insulated wires 23, 25, 27 and 29, which are marked differently in the Figure for the sake of clarity. It will be seen from FIG. 2 that the ground-connected ends of each pair of adjacent wires are located at opposite ends of the cylinder. The wires 23 and 27 are connected to the ground point 31 and the wires 25 and 29 are connected to the ground point 33. The advantage of this embodiment over that of FIG. 1 resides in the fact that the turns of the separate wires are spaced further apart so that the inductance is even further reduced. I

FIG. 3 shows the screening coil 1 disposed between .vertical deflection coil 40 and horizontal deflection coil 42. All of the coils 1, 40 and 42 are about a camera tube 44.

What is claimed is:

l. A deflection unit for an electron beam device comprising, a line deflection coil and a frame deflection coil mounted on said electron beam means, and at least one device for electric screening which does not disturb magnetic fields and which comprises a hollow cylindrical cage composed mainly of electrically conductive material mounted on said electron beam device, said cage comprising at least two wires helically wound in a multifilar fashion with one end of each wire connected to ground and the ground-connected ends of each pair of adjacent wires being located at opposite ends of the cylindrical cage.

2. A deflection unit as claimed in claim 1, wherein said wires of the cage are insulated and are located in compact turns in the plane of the cylindrical wall.

3. A deflection unit as claimed in claim 1 wherein one of the wire ends to be connected to ground is extended at one end of the cylinder and is passed back to the other end where all ends in common are connected to ground.

4. A deflection unit as claimed in claim 1 wherein the multifilar wires of the cage are disposed between the line and frame deflection coils on said electron beam device.

22253? UNITED STATES PATENT OFFICE "CERTIFICATEOF CORRECTION-n Patent No. 3 824,51 5 Dated July v1.6, 1974 Invencor(s) aENEDIcTUs T, J. HoLmN It is certifiedthattk error appears in. the above-identified patent and that said Letters Patent are hereby corrected as shown below:

r I IN THE TITLE PAGE;

b elow "inventor". insert Assignee: U,S. Philips Corporation, New York, N.Y.

Signed and sealed this. 22nd day of October 1974.

(SEAL) Attest: v I

Mc-COY M. GIBSON JR. C.'MARSHALi. DANN Attesting Officer 7 Commissioner of Patents 2;;2? UNITED STATES PATENT OFFICE I CERTIFICATE OF CORRECTION Patent No. 3 824,515 Dated July .16, 1974 Inventofls) BENEDICTUSIT. :J. HOLMHN It is certified tha 't errorappears in the above-identified patent and that: said Letters Patent are hereby corrected as shown below:

T- v IN THE TITLE PAGE;

below "Inventor" insert Assignee: U.S. Philips Corporation, New York, N.Y.

Signed and sealed this. 22nd day of October 1974.

(SEAL) Attest: v

McCOY M. GIBSON JR. j CQMARSHALL DANN Attesting Officer Commissioner of Patents 

1. A deflection unit for an electron beam device comprising, a line deflection coil and a frame deflection coil mounted on said electron beam means, and at least one device for electric screening which does not disturb magnetic fields and which comprises a hollow cylindrical cage composed mainly of electrically conductive material mounted on said electron beam device, said cage comprising at least two wires helically wound in a multifilar fashion with one end of each wire connected to ground and the ground-connected ends of each pair of adjacent wires being located at opposite ends of the cylindrical cage.
 2. A deflection unit as claimed in claim 1, wherein said wires of the cage are insulated and are located in compact turns in the plane of the cylindrical wall.
 3. A deflection unit as claimed in claim 1 wherein one of the wire ends to be connected to ground is extended at one end of the cylinder and is passed back to the other end where all ends in common are connected to ground.
 4. A deflection unit as claimed in claim 1 wherein the multifilar wires of the cage are disposed between the line and frame deflection coils on said electron beam device. 